PROJECT SUMMARY Worldwide more than 90% of all HIV infections occur via mucosal route. The gastrointestinal tract is a site of massive CD4 T-cell depletion, viral infection, enterocyte apoptosis, disruption of epithelial tight junctions leading to microbial translocation, and lymphoid tissue fibrosis. The SIV infected rhesus macaque (RM) model is considered a well-accepted model to study of HIV-associated enteropathy and we have recently discovered that intestinal epithelial cell (iEC) apoptosis and diminished iEC regeneration occur soon after SIV-infection. Internalization of IL-10R with the resultant impact on IL-10 signaling and dysregulation of the IL-10-mediated anti-inflammatory responses also play a crucial role in iEC damage and subsequent SIV pathogenesis. Understanding the aberrant iEC regeneration in HIV/SIV might lead to an alternative approach for the treatment of HIV-mediated enteropathy based on enhancing iEC repair mechanisms. In the small intestine, each intestinal villus is encircled by at least six crypts of Lieberkhn, which house dedicated populations of stem and progenitor cells that self-renew, as well as give rise to the various differentiated iECs. LGR5+ (Leu- rich repeat containing G protein-coupled receptor 5) was identified as the marker for crypt base columnar (CBC) stem cells that was selectively expressed at the base of adult intestinal crypts. Genetic analysis of LGR5+ intestinal stem cells (ISCs) revealed that a single stem cell leads to crypt homeostasis in adult intestines by clonal expansion. Stem cells give rise to the polarized enterocytes, goblet cells, enteroendocrine cells, and tuft cells that migrate up to the villi after passing through several transiently-amplifying (TA) stages. TA cells also terminally differentiate into Paneth cells (PCs), a highly specialized secretory cell type which intersperse with stem cells at the base of the crypts in the small intestine. Recent cell ablation and co-culture studies showed that PCs provide essential niche signals to support LGR5+ stem cell renewal and survival. Therefore, we hypothesize that HIV/SIV infection disrupts the communication between LGR5+ ISC and PCs leading to diminished iECs regeneration. In Aim 1, we will define the correlates of LGR5+ stem cells and PCs with SIV/HIV infection status. In Aim 2, we will uncover the alterations of ISCs and PCs communication in SIV infection in two sub aims. In Sub-Aim 2a, we will determine the transcriptional programming of ISCs and PCs in normal and SIV infected RMs. In Sub-Aim 2b, we will compare the colony forming efficiency of rhesus intestinal LGR5+ stem cells between SIV infected and normal RMs.